Shown in printed publication DE 101 52 414 A1 and in printed publication DE 197 23 624 A1 are hydraulic actuating devices for adjusting valve bodies with a fixed mechanical coupling between a cylinder and the valve body. The valve body is pretensioned into the closed position of the valve by means of an emergency spring, via which the valve can be closed during an emergency operation.
It is disadvantageous to such hydraulic actuating devices that with each adjustment movement of the valve body by means of the actuating device the emergency spring is relaxed or tensioned.
Printed publication DE 103 08 017 B4 shows a hydraulic actuating device with a mechanical coupling device and with an emergency spring, wherein during a control operation or normal operation the emergency spring in the tensioned state is moved together with the coupling device. When the emergency closing function is activated, a bell-crank lever device is activated so that the emergency spring is relaxed and the mechanical coupling device is expanded or extended in the process. As a result, the valve is closed.
A disadvantage of the last-named actuating devices is the equipment-engineering cost for the mechanical activation function which has to be together with movement of the emergency spring during normal operation.
DE 10 2010 011 516 A1 shows a hydraulic actuating device with a mechanical coupling device, wherein during normal operation the emergency spring in the tensioned state is moved along with the coupling device. During emergency operation, a locking device, which keeps the emergency spring in the tensioned state, is activated so that the emergency spring is relaxed and the coupling device is expanded or extended in the process. As a result, the valve is closed. Proposed for this is a hydraulic locking device with two pistons which during normal operation are pressed against each other via pressure medium, wherein during emergency operation the pressure medium is relieved and the pressing is terminated.
A disadvantage of such hydraulic adjusting devices is the equipment-engineering cost on the one hand for the hydraulics which are required for the positioning control, and on the other hand for the hydraulics which are required for the locking device, which cost can be recognized by two separate cylinders, for example.